CN115976642A - High-quality silicon carbide single crystal substrate, and preparation method and detection method thereof - Google Patents
High-quality silicon carbide single crystal substrate, and preparation method and detection method thereof Download PDFInfo
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Abstract
The invention provides a high-quality silicon carbide single crystal substrate, which is observed in a microscope dark field mode, wherein the observation is performed in a state of a 10-time objective lens and a magnification factor higher than the objective lens, and the density of bright spots is less than 10cm ‑2 . Compared with the prior art, the substrate prepared from the silicon carbide single crystal provided by the invention has low internal defect density, and when a device is prepared on the silicon carbide single crystal substrate, on one hand, the yield of the device is high, and on the other hand, the performance index of the prepared device is excellent.
Description
Technical Field
The invention belongs to the technical field of semiconductor materials, and particularly relates to a high-quality silicon carbide single crystal substrate, and a preparation method and a detection method thereof.
Background
The third-generation semiconductor material is a wide-bandgap semiconductor material represented by silicon carbide and gallium nitride, and has the advantages of high breakdown electric field, high thermal conductivity, high electronic saturation rate, strong radiation resistance and the like, so that a semiconductor device prepared by the third-generation semiconductor material can stably operate at higher temperature, is suitable for high-voltage and high-frequency scenes, and can obtain higher operation capacity with less electric energy consumption.
In recent years, silicon carbide single crystals have been widely used for manufacturing high-temperature, high-frequency and high-power electronic devices by virtue of their characteristics of large forbidden bandwidth, strong critical breakdown field, high thermal conductivity, high saturation drift velocity and the like. With the widespread use of silicon carbide single crystals, the research on silicon carbide single crystals is more and more intensive, so that the macroscopic structural defect density in the bulk silicon carbide single crystal is continuously reduced, including defects such as micropipes, polytype inclusions and large-particle inclusions. However, some microscopic defects still exist, and relatively high densities exist, which are difficult to eliminate. The presence of these defects can result in low device yields and undesirable device performance characteristics, and thus, it remains a desirable goal to reduce or eliminate the microscopic defect density to improve device yield and performance characteristics.
Disclosure of Invention
In view of the above, the present invention provides a high quality silicon carbide single crystal substrate with a very low micro defect density, a method for manufacturing the same, and a method for inspecting the same.
The invention provides a high-quality silicon carbide single crystal substrate, which is observed in a microscope dark field mode, wherein the observation is performed in a state of a 10-time objective lens and a magnification factor higher than the objective lens, and the density of bright spots is less than 10cm -2 (ii) a Preferably, the high-quality silicon carbide single crystal substrate has a diameter of 4 inches, or 6 inches, or 8 inches, and a thickness of 200 micrometers to 600 micrometers.
Preferably, the observation is in a dark field mode at 20 times objective lens and above magnification state;
preferably, the objective state is 50 times in dark field mode.
Preferably, the density of the bright spots is less than 2cm -2 ；
Preferably, the density of the bright spots is less than 0.5cm -2 ；
Preferably, the density of the bright spots is 0.
The invention also provides a preparation method of the high-quality silicon carbide single crystal substrate, which comprises the following steps:
placing silicon carbide powder at the bottom of the closed space, fixing seed crystals at the top of the closed space, wherein the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystals is more than or equal to 3; the ratio of the height of the silicon carbide powder to the diameter of the seed crystal is less than or equal to 0.3;
a growth chamber is arranged between the silicon carbide powder and the seed crystal, a graphite assembly is arranged on the side wall of the growth chamber, the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom, and the silicon carbide single crystal substrate is obtained by heating and growing in a protective atmosphere.
Preferably, a filter layer structure consisting of diamond single crystals and/or diamond polycrystalline particle layers is arranged between the silicon carbide powder and the seed crystals.
Preferably, the filter layer structure is composed of diamond monocrystal and/or diamond polycrystalline particle layers, wherein the size of the diamond monocrystal and/or diamond polycrystalline particle is between 5 micrometers and 5 millimeters, preferably between 10 micrometers and 3 millimeters, and more preferably between 50 micrometers and 2 millimeters; the layer of monocrystalline and/or polycrystalline diamond particles has a bulk density of 1.5 grams per cubic centimeter or more, preferably 1.8 grams per cubic centimeter or more, and more preferably 2.1 grams per cubic centimeter or more.
Preferably, the filter layer structure is composed of diamond single crystal and/or diamond polycrystalline particle layers, wherein the thickness of the diamond single crystal and/or diamond polycrystalline particle layers is between 5mm and 30 mm, preferably between 10mm and 20 mm; preferably, the layer of diamond single crystals and/or polycrystalline diamond particles is divided into two layers, each layer accounting for 50% of the thickness, and the grain size of the upper layer of diamond single crystals and/or polycrystalline diamond particles is larger than that of the lower layer of diamond single crystals and/or polycrystalline diamond particles.
Preferably, the included angle between the bottom of the longitudinal section of the graphite assembly and the side wall without contact is 15-25 degrees; the length of the top of the longitudinal section of the cavity is 10-15 mm longer than the diameter of the silicon carbide seed crystal.
Preferably, the ratio of the distance between the graphite assembly and the top of the enclosed space to the height of the graphite assembly is between 0.3 and 1.
The invention also provides a detection method of the silicon carbide single crystal substrate, which is characterized in that the silicon carbide single crystal substrate is placed under a microscope, and the number and the density of the bright spots are observed in a dark field mode.
The invention also provides a growth device of the high-quality silicon carbide single crystal, which comprises a closed space;
a seed crystal placing area is arranged at the top of the closed space;
a powder placing area is arranged at the bottom of the closed space;
the ratio of the surface area of the powder placing area to the surface area of the seed crystal placing area is more than or equal to 3;
a growth chamber is arranged between the bottom and the top of the closed space;
the side wall of the growth chamber is provided with a graphite assembly, and the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom.
The present invention providesA high-quality silicon carbide single crystal substrate is observed in a dark field mode of a microscope, and the observation is performed in a state of a 10-time objective lens and a magnification of more than 10 times, and the density of bright spots is less than 10cm -2 . Compared with the prior art, the substrate prepared from the silicon carbide single crystal provided by the invention has low internal defect density, and when a device is prepared on the silicon carbide single crystal substrate, on one hand, the yield of the device is high, and on the other hand, the performance index of the prepared device is excellent.
The invention provides a preparation method of a high-quality silicon carbide single crystal substrate, which comprises the following steps: placing silicon carbide powder at the bottom of the closed space, fixing seed crystals at the top of the closed space, wherein the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystals is more than or equal to 3; the ratio of the height of the silicon carbide powder to the diameter of the seed crystal is less than or equal to 0.3; a growth chamber is arranged between the silicon carbide powder and the seed crystal, a graphite assembly is arranged on the side wall of the growth chamber, the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom, and the silicon carbide single crystal is obtained by heating and growing in a protective atmosphere.
Compared with the prior art, the graphite assembly is arranged in the growth chamber, so that the temperature gradient of a crystal growth area is reduced through higher thermal conductivity of the graphite assembly, the thermal stress of the silicon carbide crystal in the growth process is reduced, and the defects of dislocation and the like in the silicon carbide crystal are reduced; on the other hand, the crystal growth area is limited to the V-shaped structure by the graphite component, so that the cross sectional area of the airflow is gradually increased in the upward transportation process of the airflow, and the upward impact force of the airflow can be relieved.
Further preferably, the growth structure used in the present invention has: the loading area is obviously larger than the area of the seed crystal, and the loading height is obviously smaller than the diameter of the seed crystal. In an induction heating system, raw materials around the bottom are more easily carbonized to form carbon particles in the growth process of silicon carbide. According to the invention, the material level of the silicon carbide powder is set to be large enough, so that the influence caused by the carbonization of surrounding raw materials can be reduced or eliminated, and on the other hand, under the same amount of silicon carbide atmosphere, the airflow cross-sectional area is large enough, so that the upward impact force of the airflow can be remarkably reduced, the possibility that the airflow brings carbonized particles into the crystal can be remarkably reduced, the disturbance of the airflow on a growth interface can be reduced, and the high-quality silicon carbide single crystal can be obtained.
Furthermore, a filter layer structure consisting of diamond single crystal and/or diamond polycrystalline particle layers is arranged between the silicon carbide powder and the seed crystals, so that extremely trace carbonized particles in the powder can be further effectively filtered; and the silicon-carbon ratio in the atmosphere can be reduced by reacting with the silicon-rich atmosphere, so that a 4H crystal form can be stably grown, and the generation of inclusions caused by silicon segregation in the silicon-rich atmosphere is reduced. In addition, the density of the diamond single crystal is 3.5 grams per cubic centimeter, the diamond polycrystal is particles formed by polymerizing single crystals, the single crystals and the single crystals share a common crystal boundary, the density is also close to 3.5 grams per cubic centimeter, and the effect of the invention can be achieved by the polycrystal and the single crystals, and the diamond monocrystal particles are mainly discussed below, but the same is also achieved for the diamond polycrystal; the microscopic diamond particles are of a compact atomic crystal structure, and the silicon-rich atmosphere reacts with the microscopic diamond particles layer by layer from the surface, so that the microscopic diamond particles cannot be powdered in the growth process, namely, one diamond particle cannot be corroded into a plurality of fine particles and still is a single particle, and the particle size is gradually reduced along with the growth time. The porous graphite reported by the conventional technology can play a role in filtering as a filtering result, but the porous graphite is very loose in microstructure and has a plurality of cavities, even if the skeleton structure is also formed by sintering fine graphite particles through a bonding agent pore-forming agent, the density is usually only 1.0 g/cc, even if the graphite material is the graphite material, the density is usually 1.8 g/cc, in the actual growth process of the silicon carbide single crystal, the porous graphite cannot play a good anti-corrosion effect along with the extension of the growth time, the porous graphite can be rapidly powdered by silicon-rich gas, and the porous graphite is a main source of a wrapping object. In the invention, the diamond monocrystal and/or diamond polycrystalline particle layer is preferably divided into two layers, each layer accounts for 50% of the thickness, the upper layer is the diamond monocrystal and/or diamond polycrystalline particle with large particle size, and the upper layer mainly plays a role in resisting silicon vapor corrosion and secondarily plays a role in filtering; the lower layer is single crystal and/or diamond polycrystalline particles with small particle size, mainly plays a role in filtering, and secondarily plays a role in resisting silicon vapor corrosion. Therefore, a filter layer structure formed by the diamond monocrystalline particle layer is arranged between the silicon carbide powder and the seed crystal, so that the silicon carbide powder can effectively filter the extremely-micro carbonized particles in the powder in a lasting manner in the growth process; and the crystal can react with the silicon-rich atmosphere to reduce the silicon-carbon ratio of the atmosphere, so that the 4H crystal form is stably grown to reduce the defects of dislocation and the like in the crystal and simultaneously reduce the defects of inclusions generated by silicon segregation generated in the silicon-rich atmosphere.
Furthermore, the invention also provides a detection method of the silicon carbide single crystal substrate, which is characterized in that the silicon carbide single crystal substrate is placed under a microscope, and the number and the density of the bright spots are observed in a dark field mode. The detection method can effectively identify the defects of the silicon carbide wafer in the microscopic scale in vivo through the density of the bright spots, and is more direct, efficient and cost-saving than the existing method.
Drawings
FIG. 1 is a schematic view showing the structure of an apparatus for growing a high-quality silicon carbide single crystal according to the present invention;
FIG. 2 is a graph showing the relationship between dark field bright spots and dislocations and inclusions in example 1 of the present invention;
FIG. 3 is a graph showing the relationship between dark field bright spots and dislocations and inclusions in example 1 of the present invention;
FIG. 4 is a graph showing the relationship between dark field bright spots and dislocations and inclusions in example 1 of the present invention;
FIG. 5 is a micrograph of a silicon carbide single crystal substrate obtained in example 2 of the present invention;
FIG. 6 is a schematic view of conventional crucibles used in comparative examples 1 and 2 of the present invention;
FIG. 7 is a micrograph of a silicon carbide single crystal substrate obtained in comparative example 1 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a high-quality silicon carbide single crystal substrate, which is observed in a microscope dark field mode, wherein the observation is performed in a state of a 10-time objective lens and a magnification factor higher than the objective lens, and the density of bright spots is less than 10cm -2 。
Wherein the diameter of the high-quality silicon carbide single crystal substrate is preferably 4 to 8 inches; specifically in the present invention, the high-quality silicon carbide single crystal substrate has a diameter of 4 inches, 6 inches, or 8 inches.
The thickness of the high-quality silicon carbide single crystal substrate is preferably 200 to 600 μm.
The crystal form of the high-quality silicon carbide single crystal is preferably 4H, 6H or 15R.
The microscope is preferably an optical microscope; the observation is preferably performed in a state of an objective lens of 10 times or more, more preferably in a state of an objective lens of 20 times or more in a dark field mode, and further preferably in a state of an objective lens of 50 times in a dark field mode; the density of the bright spots is the ratio of the number of the bright spots in a certain area of the silicon carbide single crystal substrate to the area of the area.
In the invention, the method specifically comprises the following steps: the method comprises the steps of placing a silicon carbide single crystal substrate under an optical microscope, selecting an objective lens of the microscope to be 10 times or more of magnification, selecting a dark field in a mode, adjusting a diaphragm and light intensity to be maximum numerical values for observation, adjusting the focal length of the microscope to focus the focal length on a certain plane between the upper surface and the lower surface of the substrate, keeping the focal length, moving the substrate up and down or left and right, and recording and accumulating the number of bright spots in each microscope field. This number represents the number of bright spots present in the substrate in the entire plane of the detection area or substrate.
In the present invention, it is preferable that the density of the bright spots is less than 5cm -2 More preferably, the density of the bright spots is less than 2cm -2 Still more preferably, the density of the bright spots is less than 0.5cm -2 Is optimumThe density of selected bright spots is 0cm -2 。
The substrate prepared from the silicon carbide single crystal provided by the invention has low internal defect density, and when a device is prepared on the silicon carbide single crystal substrate, on one hand, the yield of the device is high, and on the other hand, the performance index of the prepared device is excellent.
The invention also provides a growing device of the high-quality silicon carbide single crystal substrate, which comprises a closed space; a seed crystal placing area is arranged at the top of the closed space; a powder placing area is arranged at the bottom of the closed space; the ratio of the surface area of the powder placing area to the surface area of the seed crystal placing area is more than or equal to 3, and the ratio of the height of the powder placing area to the diameter of the seed crystal placing area is less than or equal to 0.3; a growth chamber is arranged between the bottom and the top of the closed space; the side wall of the growth chamber is provided with a graphite assembly, and the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom.
Referring to fig. 1, fig. 1 is a schematic view of a growing apparatus of a high-quality silicon carbide single crystal according to the present invention, in which 1 is a closed space, 2 is a powder placing region, 3 is a diamond particle layer, 4 is a growing chamber, 5 is a graphite assembly, and 6 is a seed crystal placing region.
The growth device of the high-quality silicon carbide single crystal comprises a closed space; the closed space is preferably a crucible, and is more preferably a graphite crucible; the graphite crucible preferably has an impurity content of less than 50ppm.
A seed crystal placing area is arranged at the top of the closed space and used for placing silicon carbide seed crystals; the growing device provided by the invention preferably further comprises a graphite bottom support, and the silicon carbide seed crystal is fixed in the seed crystal placing area through the graphite bottom support; the graphite shoe preferably has an impurity content of less than 50ppm.
And a powder placing area is arranged at the bottom of the closed space and used for placing silicon carbide powder.
A growth chamber is arranged between the bottom and the top of the closed space, namely a growth chamber is arranged between the seed crystal placing area and the powder placing area; a graphite assembly is arranged on the side wall of the growth chamber; the graphite component preferably has an impurity content of less than 50ppm; the included angle between the bottom of the longitudinal section of the graphite assembly and the side wall, which is not contacted with the bottom of the longitudinal section of the graphite assembly, is preferably 15-25 degrees, more preferably 18-22 degrees, and further preferably 20 degrees; the graphite components on the side wall jointly enclose a cavity; the longitudinal section of the cavity is preferably a trapezoid with a wide top and a narrow bottom; the center of the longitudinal section of the cavity and the center of the seed crystal placing area are preferably positioned in a plane vertical to the bottom of the closed space; the length of the top of the longitudinal section is preferably 10-15 mm longer than the diameter of the seed crystal placing area; the ratio of the distance between the graphite component and the top of the closed space to the height of the graphite component is preferably 0.3 to 1; in the present invention, the height of the graphite assembly is preferably 10 to 15mm.
The growth device provided by the invention preferably further comprises a filter layer structure consisting of diamond single crystals and/or diamond polycrystalline particle layers; the filtering layer consisting of the diamond single crystal and/or diamond polycrystalline particle layer is arranged between the powder placing area and the graphite component, and is more preferably arranged on the surface of the silicon carbide powder placed in the powder placing area; the filter layer structure is composed of diamond single crystal and/or diamond polycrystalline particle layers, wherein the size of the diamond single crystal and/or diamond polycrystalline particle is between 5 micrometers and 5 millimeters, preferably between 10 micrometers and 3 millimeters, and more preferably between 50 micrometers and 2 millimeters; the bulk density of the layer of diamond single crystals and/or diamond polycrystalline particles is above 1.5 grams per cubic centimeter, preferably above 1.8 grams per cubic centimeter, more preferably above 2.1 grams per cubic centimeter; the thickness of the diamond single crystal and/or diamond polycrystalline particle layer is between 5mm and 30 mm, preferably between 10mm and 20 mm; in the present invention, the layer of diamond single crystals and/or diamond polycrystalline particles is preferably divided into two layers; the thickness of the upper layer is preferably 30 to 70% of the overall thickness, more preferably 40 to 60%, and the most preferred two layers in the present invention are each 50% of the thickness; the grain size of the diamond single crystal and/or the diamond polycrystalline particles on the upper layer is larger than that of the diamond single crystal and/or the diamond polycrystalline particles on the lower layer, namely, the diamond particles with large grain sizes are on the upper layer, and the diamond particles with small grain sizes are on the lower layer.
The invention also provides a preparation method of the high-quality silicon carbide single crystal, which comprises the following steps: placing silicon carbide powder at the bottom of the closed space, fixing silicon carbide seed crystals at the top of the closed space, wherein the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystals is more than or equal to 3; the ratio of the height of the silicon carbide powder to the diameter of the seed crystal is less than or equal to 0.3; a growth chamber is arranged between the silicon carbide powder and the seed crystal, a graphite assembly is arranged on the side wall of the growth chamber, and the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom; heating and growing in the protective atmosphere to obtain the silicon carbide single crystal.
Wherein, the sources of all raw materials are not specially limited and can be sold in the market; the present invention is preferably prepared using the above-described growing apparatus.
Placing silicon carbide powder at the bottom of the closed space, and fixing silicon carbide seed crystals at the top; the closed space is the same as the above, and is not described again; the silicon carbide seed crystal is preferably a polished silicon carbide seed crystal; the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystal is preferably greater than or equal to 3, and more preferably 3-5; in the embodiment provided by the invention, the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystal is specifically 3.5; the ratio of the height of the silicon carbide powder to the diameter of the silicon carbide seed crystal is preferably less than or equal to 0.3, more preferably 0.05 to 0.3, still more preferably 0.1 to 0.3, and most preferably 0.2 to 0.3; in the embodiment provided by the invention, the ratio of the height of the silicon carbide powder to the diameter of the silicon carbide seed crystal is specifically 0.25; the material charging structure is characterized in that the bottom silicon carbide powder has large area and low height, on one hand, in an induction heating system, the peripheral raw materials at the bottom are easy to be carbonized to form carbonized particles, and the influence caused by the carbonization of the peripheral raw materials can be reduced or eliminated by arranging the material surface of the silicon carbide powder to be large enough, and on the other hand, by arranging the surface area of the bottom silicon carbide powder to be large enough, the upward impact force of airflow can be remarkably reduced due to the large enough cross-sectional area of the airflow under the silicon carbide atmosphere with the same amount, so that the possibility that the carbonized particles are brought into crystals by the airflow can be remarkably reduced.
A growth chamber is arranged between the silicon carbide powder and the seed crystal, a graphite assembly is arranged on the side wall of the growth chamber, and the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom; the growth chamber, graphite assembly and cavity are as described above and will not be described further herein.
Heating and growing in a protective atmosphere to obtain silicon carbide single crystals; the method of heating growth is known to those skilled in the art, and is not limited in any way, and can be according to the method disclosed in chinese patent publication nos. CN105463575B and CN110983434B or the method disclosed in WO2022110265 A1; in the invention, preferably, the vacuum pumping is carried out, then the protective atmosphere is introduced, and after the heating is carried out to the growth temperature, the pressure is reduced for growth; wherein the protective atmosphere is preferably introduced until the pressure is 50-80 kPa; the growth temperature is preferably 2000-2500 ℃; the pressure for growth is preferably 800 to 1200Pa, more preferably 900 to 1100Pa, and still more preferably 1000Pa; the growth time is preferably 60 to 100 hours, more preferably 70 to 90 hours, and still more preferably 80 hours.
The obtained high-quality silicon carbide single crystal is cut, ground and polished to obtain the high-quality silicon carbide single crystal substrate.
According to the invention, the graphite component is arranged in the growth chamber, so that on one hand, the temperature gradient of a crystal growth area is reduced through the higher thermal conductivity of the graphite component, thereby reducing the thermal stress in the growth process of the silicon carbide crystal and being beneficial to reducing the defects of dislocation and the like in the silicon carbide crystal; on the other hand, the graphite component limits the crystal growth area to be in a V-shaped structure, so that the cross section area of the airflow is gradually increased in the upward conveying process of the airflow, and the upward impact force of the airflow can be relieved.
Further preferably, the growth structure used in the present invention has: the loading area is obviously larger than the area of the seed crystal, and the loading height is obviously smaller than the diameter of the seed crystal. In an induction heating system, raw materials around the bottom are more easily carbonized to form carbon particles in the growth process of silicon carbide. According to the invention, the material level of the silicon carbide powder is set to be large enough, so that the influence caused by the carbonization of surrounding raw materials can be reduced or eliminated, and on the other hand, under the same amount of silicon carbide atmosphere, the airflow cross-sectional area is large enough, so that the upward impact force of the airflow can be remarkably reduced, the possibility that the airflow brings carbonized particles into the crystal can be remarkably reduced, the disturbance of the airflow on a growth interface can be reduced, and the high-quality silicon carbide single crystal can be obtained.
Furthermore, a filter layer structure consisting of diamond single crystal and/or diamond polycrystalline particle layers is arranged between the silicon carbide powder and the seed crystals, so that extremely trace carbonized particles in the powder can be further effectively filtered; and the silicon-carbon ratio in the atmosphere can be reduced by reacting with the silicon-rich atmosphere, so that a 4H crystal form can be stably grown, and the generation of inclusions caused by silicon segregation in the silicon-rich atmosphere is reduced. In addition, the density of the diamond single crystal is 3.5 g/cubic centimeter, the diamond single crystal is a compact atomic crystal structure on a microcosmic scale, and the silicon-rich atmosphere reacts with the silicon-rich atmosphere layer by layer from the surface, so that the diamond single crystal cannot be powdered in the growth process, namely, one diamond particle cannot be corroded into a plurality of fine particles and still is a single particle, and the particle size is gradually reduced along with the extension of the growth time. The porous graphite reported by the conventional technology can play a role in filtering as a filtering result, but the porous graphite is very loose in microstructure and has a plurality of cavities, even if the skeleton structure is also formed by sintering fine graphite particles through a bonding agent pore-forming agent, the density is usually only 1.0 g/cc, even if the graphite material is the graphite material, the density is usually 1.8 g/cc, in the actual growth process of the silicon carbide single crystal, the porous graphite cannot play a good anti-corrosion effect along with the extension of the growth time, the porous graphite can be rapidly powdered by silicon-rich gas, and the porous graphite is a main source of a wrapping object. Preferably, the diamond monocrystal and/or diamond polycrystalline particle layer is divided into two layers, each layer accounts for 50% of the thickness, the upper layer is diamond particles with large particle sizes, the diamond particles mainly play a role in resisting silicon vapor corrosion, and the diamond particles secondarily play a role in filtering; the lower layer is small-particle diamond which mainly plays a role in filtering and secondarily plays a role in resisting silicon vapor corrosion. Therefore, a filter layer structure consisting of diamond single crystals and/or diamond polycrystalline particle layers is arranged between the silicon carbide powder and the seed crystals, so that the silicon carbide powder can effectively filter extremely trace carbonized particles in the powder in a lasting manner in the growth process; and the crystal can grow and react with the silicon-rich atmosphere, so that the silicon-carbon ratio of the atmosphere is reduced, the 4H crystal form is stably grown, and the silicon segregation generated in the silicon-rich atmosphere is reduced to generate a inclusion.
The invention also provides a detection method of the silicon carbide single crystal, which is characterized in that the silicon carbide single crystal substrate is placed under a microscope, and the number and the density of the bright spots are observed in a dark field mode.
The microscope is preferably an optical microscope; the observation is preferably performed in a state of an objective lens of 10 times or more, more preferably in a state of an objective lens of 20 times or more in a dark field mode, and further preferably in a state of an objective lens of 50 times in a dark field mode; the density of the bright spots is the ratio of the number of the bright spots in a certain area of the silicon carbide single crystal to the area of the area.
In the invention, the method specifically comprises the following steps: the method comprises the steps of placing a silicon carbide single crystal substrate under an optical microscope, selecting an objective lens of the microscope to be 10 times or more of magnification, selecting a dark field in a mode, adjusting a diaphragm and light intensity to be maximum numerical values for observation, adjusting the focal length of the microscope to focus the focal length on a certain plane between the upper surface and the lower surface of the single crystal substrate, keeping the focal length, moving the single crystal substrate up and down or left and right, and recording and accumulating the number of bright spots in each microscope field of view. This number represents the number of bright spots present in the substrate in the detection area or the entire plane of the substrate.
The CS920 for testing KLA conventionally tests the surface of a wafer through laser, only can identify the defects on the surface of the SiC wafer, and cannot effectively identify the defects such as internal crystal dislocation, small-angle grain boundary, fine inclusion, micron-level plane hexagonal cavity and the like. The KOH etching is a destructive test, only dislocation can be identified, and the wrapping object in the body can not be effectively identified. The detection method can effectively identify the defects of the silicon carbide wafer in the microscopic scale in vivo through the density of the bright spots, and is more direct, efficient and cost-saving than the existing method.
In order to further illustrate the present invention, a high-quality silicon carbide single crystal substrate, a method for producing the same, and a method for inspecting the same according to the present invention will be described in detail with reference to examples.
The reagents used in the following examples are all commercially available.
Example 1
The mode of the microscope is selected as a Dark Field (DF) by using an Olympus optical microscope MX63, the diaphragm is adjusted to be maximum, the light intensity is adjusted to be maximum, and the obtained relationship graphs of dark field bright spots, dislocation and wrappage are shown in figures 2-4. Wherein, the left image in FIG. 2 is a dislocation dense area, and the right image is a bright spot dense area observed under the dark field condition of the microscope at the corresponding position; in FIG. 3, the left image is a scattered dislocation region, and the right image is a scattered bright point observed under the dark field condition of a microscope at a corresponding position; in fig. 4, the left image is a line of small particle packing, and the right image is a line of bright spots observed under the dark field condition of the microscope at the corresponding position. And the obtained silicon carbide single crystal substrate is subjected to black spot or abnormal bright spot test and statistics by using a conventional microscope bright field (an Olympus microscope is adopted, the objective lens is selected by 10 times, and detection is carried out in a bright field mode), and basically no defect is observed.
Through a great deal of research, bright spots detected by a microscope dark field mainly correspond to microscopic defects with larger internal dimensions of the SiC crystal, such as composite dislocations, dislocation dense regions, dislocation lines, and small-angle grain boundaries, inclusions of micron-sized carbon or silicon. Further research finds that defects of these scales are just defects having a significant influence on the performance of the SiC semiconductor device, and as shown in table 1, the average density of bright spots has a direct correspondence with device failure and SBD device yield of 1200V 50A.
TABLE 1 relationship between average density of bright spots and device yield
Example 2
Taking a piece of the sample, under the dark field condition of a microscope, the density of bright points is 1cm -2 The 6-inch seed crystal of the 4H crystal form grows by adopting the C surface of the seed crystal. Taking a crucible as shown in figure 1, filling silicon carbide powder at the bottom of the crucible, wherein the ratio of the upper surface area of the silicon carbide powder to the surface area of the seed crystal is 3.5, and the filling height of the silicon carbide powder and the seed crystalThe diameter ratio of the crystal is 0.25, the upper part of the silicon carbide powder is provided with a filter layer structure consisting of a diamond single crystal particle layer, the filter layer structure consists of two layers of diamond particles, the upper layer is large particle size, the particle size is 0.6mm, the lower layer is small particle size, the particle size is 0.2mm, the thicknesses of the two layers are respectively 8mm, the stacking density of the particle layer is 2.3 g per cubic centimeter, a graphite assembly is placed above the filter layer, the graphite assembly is arranged at the position of 5mm below a crucible cover, the height of the graphite assembly is 15mm, the inner diameter of the upper part of the graphite assembly is 10mm larger than that of the silicon carbide seed crystal, the theta angle is 20 degrees, and the silicon carbide long crystal furnace is assembled and placed in the silicon carbide long crystal furnace as shown in figure 1. Vacuumizing the system, then filling argon into the system until the pressure of a hearth reaches 80kPa, heating the system to 2300 ℃, gradually reducing the pressure of the hearth to 1000Pa, feeding mixed gas of argon and nitrogen (the nitrogen accounts for 10%), keeping the pressure of the hearth constant at 1000Pa by a pressure control system, starting to grow silicon carbide, obtaining 6-inch conductive silicon carbide crystals after 80 hours of growth, and cutting, grinding and polishing the crystals to obtain the 6-inch conductive silicon carbide single crystal substrate.
Testing and counting the bright spots of the obtained silicon carbide single crystal substrate at the later growth stage by using a microscope dark field (using an Olympus microscope, selecting an objective lens by 10 times, and detecting in a dark field mode), wherein the test result shows that the bright spot density is 0.1cm -2 After the density of the bright spots is tested, the substrate is etched by KOH solution, dislocation statistics is carried out, and the substrate dislocation test result is as follows: TSD-52cm -2 ，TED-1350cm -2 ，BPD-180cm -2 ，EPD-1582cm -2 。
Example 3
Taking a 6-inch seed crystal of 4H crystal form with the bright spot density of 5 under the dark field condition of a microscope, and growing by adopting a C surface of the seed crystal. Taking a crucible as shown in figure 1, filling silicon carbide powder with a 3C crystal form at the bottom of the crucible, wherein the ratio of the surface area of the silicon carbide powder to the surface area of seed crystals is 3.5, the ratio of the charging height of the silicon carbide powder to the diameter of the seed crystals is 0.25, arranging a filter layer structure consisting of diamond monocrystalline particle layers on the upper part of the silicon carbide powder, wherein the filter layer structure consists of two layers of diamond particles, the upper layer is large in particle size and 0.7mm in particle size, the lower layer is small in particle size and 0.3mm in particle size, the thicknesses of the two layers are respectively 4mm, the stacking density of the particle layers is 2.2 grams per cubic centimeter, placing a graphite assembly above the filter layer, the graphite assembly is arranged at a position 5mm below a crucible cover, the height of the graphite assembly is 15mm, the inner diameter of the upper part of the graphite assembly is 10mm larger than the diameter of the silicon carbide seed crystals, the theta angle is 20 degrees, and assembling and placing the graphite assembly into a silicon carbide crystal growth furnace as shown in figure 1. Vacuumizing the system, then filling argon into the system until the pressure of a hearth reaches 80kPa, heating the system to 2300 ℃, gradually reducing the pressure of the hearth to 1000Pa, feeding mixed gas of argon and nitrogen (the nitrogen accounts for 10 percent) into the hearth, keeping the pressure of the hearth constant at 1000Pa by a pressure control system, starting to grow silicon carbide, obtaining 6-inch conductive silicon carbide crystals after 80 hours of growth, and cutting, grinding and polishing the crystals to obtain the 6-inch conductive silicon carbide single crystal substrate.
Testing and counting the bright spots of the obtained silicon carbide single crystal substrate at the later growth stage by using a microscope dark field (an Olympus microscope with 10 times of objective lens selection and detection in a dark field mode), wherein the test result shows that the density of the bright spots is 1.5cm -2 After the density of the bright spots is tested, the substrate is etched by KOH solution, dislocation statistics is carried out, and the substrate dislocation test result is as follows: TSD-320cm -2 ，TED-2860cm -2 ，BPD-420cm -2 ，EPD-3600cm -2 。
Example 4
Taking a 6-inch seed crystal of 4H crystal form with the bright spot density of 1 under the dark field condition of a microscope, and growing by adopting a C surface of the seed crystal. Taking a crucible as shown in figure 1, filling silicon carbide powder with a 3C crystal form at the bottom of the crucible, wherein the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystal is 3.5, the ratio of the charging height of the silicon carbide powder to the diameter of the seed crystal is 0.25, and assembling and placing the silicon carbide powder into a silicon carbide crystal growth furnace according to the structure shown in figure 1 without adding a diamond filter layer and a graphite assembly structure on the upper part of the silicon carbide powder. Vacuumizing the system, then filling argon into the system until the pressure of a hearth reaches 80kPa, heating the system to 2300 ℃, gradually reducing the pressure of the hearth to 1000Pa, feeding mixed gas of argon and nitrogen into the hearth, keeping the pressure of the hearth constant at 1000Pa through a pressure control system, starting to grow silicon carbide, obtaining 6-inch conductive silicon carbide crystals after 80 hours of growth, and performing cutting, grinding and polishing treatment on the crystals to obtain the 6-inch conductive silicon carbide single crystal substrate.
Testing and counting the bright spots of the obtained silicon carbide single crystal substrate at the later growth stage by using a microscope dark field (an Olympus microscope with 10 times of objective lens selection and detection in a dark field mode), wherein the test result shows that the density of the bright spots is 0.8cm -2 After the spot density is tested, KOH solution etching is carried out on the substrate, dislocation statistics is carried out, and the substrate dislocation test result is as follows: TSD-120cm -2 ，TED-2130cm -2 ，BPD-270cm -2 ，EPD-2520cm -2 。
Comparative example 1
Taking a 6-inch seed crystal of 4H crystal form with the bright spot density of 1 under the dark field condition of a microscope, and growing by adopting a C surface of the seed crystal. Taking a conventional crucible as shown in figure 6, wherein 1 is the crucible, 2 is silicon carbide powder, 3 is a growth chamber and 4 is a seed crystal in figure 6, filling silicon carbide powder with a 4H crystal form at the bottom of the crucible, wherein the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystal is 1.5, and the ratio of the charging height of the silicon carbide powder to the diameter of the seed crystal is 0.6, assembling and placing the crucible into a silicon carbide crystal growth furnace according to the scheme shown in figure 6. Vacuumizing the system, then filling argon into the system until the pressure of a hearth reaches 80kPa, heating the system to 2300 ℃, gradually reducing the pressure of the hearth to 1000Pa, feeding mixed gas of argon and nitrogen into the hearth, keeping the pressure of the hearth constant at 1000Pa through a pressure control system, starting to grow silicon carbide, obtaining 6-inch conductive silicon carbide crystals after 80 hours of growth, and performing cutting, grinding and polishing treatment on the crystals to obtain the 6-inch conductive silicon carbide single crystal substrate.
Testing and counting the bright spots of the obtained silicon carbide single crystal substrate at the later growth stage by using a microscope dark field (using an Olympus microscope, selecting an objective lens by 10 times, and detecting in a dark field mode), wherein the test result shows that the bright spot density is 25cm -2 After testing the density of the light spot, the substrate is etched by KOH solutionEtching and dislocation statistics are carried out, and the substrate dislocation test result is as follows: TSD-1035cm -2 ，TED-5320cm -2 ，BPD-1850cm -2 ，EPD-8205cm -2 。
Comparative example 2
Taking a 6-inch seed crystal of 4H crystal form with the bright spot density of 5 under the dark field condition of a microscope, and growing by adopting a C surface of the seed crystal. A conventional crucible as shown in figure 6 is taken, silicon carbide powder with a 4H crystal form is filled at the bottom of the crucible, the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystal is 1.5, the ratio of the charging height of the silicon carbide powder to the diameter of the seed crystal is 0.6, and the crucible is assembled and placed into a silicon carbide crystal growth furnace as shown in figure 6. Vacuumizing the system, then filling argon into the system until the pressure of a hearth reaches 80kPa, heating the system to 2300 ℃, gradually reducing the pressure of the hearth to 1000Pa, feeding mixed gas of argon and nitrogen into the hearth, keeping the pressure of the hearth constant at 1000Pa through a pressure control system, starting to grow silicon carbide, obtaining 6-inch conductive silicon carbide crystals after 80 hours of growth, and performing cutting, grinding and polishing treatment on the crystals to obtain the 6-inch conductive silicon carbide single crystal substrate.
Testing and counting the bright spots of the obtained silicon carbide single crystal substrate at the later growth stage by using a microscope dark field (an Olympus microscope with 10 times of objective lens selection and detection in a dark field mode), wherein the test result shows that the density of the bright spots is 30cm -2 After the density of the bright spots is tested, the substrate is etched by KOH solution, dislocation statistics is carried out, and the substrate dislocation test result is as follows: TSD-1840cm -2 ，TED-7250cm -2 ，BPD-2320cm -2 ，EPD-11410cm -2 。
Claims (12)
1. A high-quality silicon carbide single crystal substrate, characterized in that the high-quality silicon carbide single crystal substrate is observed in a dark field mode of a microscope, the observation is performed in a state of a 10-fold objective lens and a magnification of more than the objective lens, and the density of bright spots is less than 10cm -2 (ii) a Preferably, the high-quality silicon carbide single crystal substrate has a diameter of 4 inches, or 6 inches, or 8 inches, and a thickness of 200 micrometers to 600 micrometers.
2. A high-quality silicon carbide single crystal substrate according to claim 1, wherein said observation is performed in a state of 20 times the magnification of the objective lens in a dark field mode and above, preferably, in a state of 50 times the magnification of the objective lens in a dark field mode.
3. A high-quality silicon carbide single crystal substrate according to claim 1, wherein the density of bright spots is less than 2cm -2 Preferably the density of bright spots is less than 0.5cm -2 More preferably, the density of the bright spots is 0.
4. A method for producing a high-quality silicon carbide single crystal substrate, characterized by comprising:
placing silicon carbide powder at the bottom of the closed space, fixing seed crystals at the top of the closed space, wherein the ratio of the surface area of the silicon carbide powder to the surface area of the seed crystals is more than or equal to 3; the ratio of the height of the silicon carbide powder to the diameter of the seed crystal is less than or equal to 0.3;
a growth chamber is arranged between the silicon carbide powder and the seed crystal, a graphite assembly is arranged on the side wall of the growth chamber, and the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom;
heating and growing in a protective atmosphere to obtain the silicon carbide single crystal substrate.
5. A preparation method according to claim 4, wherein a filter layer structure composed of a layer of single crystals of diamond and/or polycrystalline particles of diamond is provided between the silicon carbide powder and the seed crystal.
6. The method according to claim 5, wherein the filter layer structure is composed of diamond single crystals and/or diamond polycrystalline particles, wherein the size of the diamond single crystals and/or diamond polycrystalline particles is between 5 micrometers and 5 millimeters, preferably between 10 micrometers and 3 millimeters, and more preferably between 50 micrometers and 2 millimeters; the layer of monocrystalline and/or polycrystalline diamond particles has a bulk density of 1.5 grams per cubic centimeter or more, preferably 1.8 grams per cubic centimeter or more, and more preferably 2.1 grams per cubic centimeter or more.
7. The method according to claim 5, wherein the filter layer structure is composed of layers of diamond single crystals and/or diamond polycrystalline particles, wherein the thickness of the layers of diamond single crystals and/or diamond polycrystalline particles is between 5mm and 30 mm, preferably between 10mm and 20 mm; preferably, the layer of diamond single crystals and/or diamond polycrystalline particles is divided into two layers, each layer accounts for 50% of the thickness, and the grain size of the diamond single crystals and/or diamond polycrystalline particles on the upper layer is larger than that of the diamond single crystals and/or diamond polycrystalline particles on the lower layer.
8. The preparation method according to claim 4, wherein the included angle between the bottom of the longitudinal section of the graphite assembly and the side wall is 15-25 degrees; the length of the top of the longitudinal section of the cavity is 10-15 mm longer than the diameter of the silicon carbide seed crystal.
9. The method for preparing according to claim 4, wherein the ratio of the distance between the graphite assembly and the top of the enclosed space to the height of the graphite assembly is between 0.3 and 1.
10. A producing method according to claim 4, wherein said silicon carbide seed crystal has a bright spot density of less than 10cm -2 Preferably less than 2cm -2 。
11. A method for detecting a silicon carbide single crystal substrate is characterized in that the silicon carbide single crystal substrate is placed under a microscope, and the number and density of existing bright spots are observed in a dark field mode.
12. A growth apparatus for a high-quality silicon carbide single crystal, comprising a closed space;
a seed crystal placing area is arranged at the top of the closed space;
a powder placing area is arranged at the bottom of the closed space;
the ratio of the surface area of the powder placing area to the surface area of the seed crystal placing area is more than or equal to 3;
a growth chamber is arranged between the bottom and the top of the closed space;
the side wall of the growth chamber is provided with a graphite assembly, and the longitudinal section of a cavity defined by the graphite assembly is a trapezoid with a wide top and a narrow bottom.
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| CN116577340B (en) * | 2023-05-28 | 2024-01-05 | 兰州大学 | Method for distinguishing threading screw dislocation and threading edge dislocation in silicon carbide |
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